The present invention relates generally to a method for producing a structured layer of a first material and more particularly to a method for producing a structured layer of a first material having at least one recess of a predetermined geometrical shape on a substructure which may be structured, if necessary.
The substructure used in such a method includes at least one second material, with one of the materials being a metal oxide superconductor material having a high transition temperature and which is sensitive to solvents containing acids. The first material is to be applied to the substructure in an atmosphere containing oxygen at an elevated deposition temperature that is between 150.degree. C. and 1000.degree. C. Such a known method is disclosed, for example, in DE-OS 38 22 905.
Superconductive metal oxide compounds having high transition temperatures T.sub.c, particularly above 77.degree. K. which can therefore be cooled with liquid nitrogen, have been generally known for several years. Corresponding high-temperature superconductor materials, which will be herein referred to as "HTSC materials", are based, for example, on a system having at least four components of the type Me1-Me2-Cu-O, where the component Me1 contains at least a rare earth metal including yttrium and the component Me2 contains at least an earth alkali metal. The primary representative of this group is the system Y-Ba-Cu-O. In addition, phases of five-component cuprates, such as the system Bi-Sr-Ca-Cu-O or Tl-Ba-Ca-Cu-O, also exhibit transition temperatures T.sub.c above 77.degree. K.
For the production of multi-layer structures with thin films made of known HTSC materials, it is necessary to be able to form structured insulator layers and/or structured HTSC layers on a suitable substructure without damaging the HTSC material while adhering to the conditions necessary for epitaxis or at least texturization patterning. Known insulator materials suitable for use as HTSC materials include, for example, SrTiO.sub.3, LaAlO.sub.3, NdGaO.sub.3, MgO and ZrO.sub.2. Texturization of a corresponding insulator layer which grows epitaxially on an HTSC layer at a high temperature, for example at 800.degree. C., is practically impossible with chemical or physical chemical methods, such as wet chemical etching or reactive ion etching. This is because all known etchants which attack the insulator material also destroy the HTSC material. For example, the known superconductor material Y-Ba-Cu-O is so sensitive to acids that it can be structured with wet chemicals using phosphoric acid in an acid/water concentration of 1/100. Furthermore, all insulator materials known for use in HTSC technology which are capable of epitaxis are difficult to dissolve, or do not dissolve at all, even in concentrated acids.
Therefore, attempts have been made to structure insulator layers by means of ion beam etching. With such a method, however, it is very difficult to determine the etching time once the HTSC material is exposed. Furthermore, this etching process can only be used if the insulator layer has a uniform thickness throughout. Also, only etching masks that are resistent to ion beams, and particularly those made of metal, can be used. In addition, the technical effort required for the structuration step is relatively great, since the work has to be carried out in a high-vacuum chamber that has a large-area ion beam.
DE-OS 38 22 905, for example, which was mentioned above, discloses the method of vacuum evaporating the insulator material through a process mask to be applied to the HTSC material, more or less floating on it. In this case, the mask has to be fixed in place with great precision, which is in the .mu.m range, and it cannot slip or become damaged even when under very great thermal stress, such as occurs during the required temperature transition from room temperature to approximately 800.degree. C. Since masks which make contact change the local temperature of the layer underneath them, problems due to heat accumulation, which may lead to the destruction of the HTSC film, cannot be prevented.
The problem with the prior art is that no method can produce a structured layer of an HTSC material or an insulator material on a preselected, possibly structured substructure used in HTSC technology, without the occurrence of any damage or destruction of the HTSC material.